This invention relates to the flow of fluid through a downhole tool positioned in a wellbore. More particularly, this invention relates to controlling torque generated by fluids flowing through downhole tools during wellbore operations.
Downhole drilling operations, such as those performed in the drilling and/or production of hydrocarbons, typically employ drilling muds to cool the drill bit as the drilling tool advanced into the wellbore. As the drilling mud passes through the downhole tool, the flow of the mud may be used to operate turbines, sirens, modulators or other components in the downhole tool. These components are typically used in downhole operations, such as well logging, measurement while drilling (MWD), logging while drilling (LWD) and other downhole operations.
The flow of fluid through the downhole tool and across rotatable components in the downhole tool generates a torque. In an axial turbine, the torque is known to scale as the square of the flow rate. The torque generated by the fluid flow across rotor blades in downhole components, sometimes referred to as xe2x80x9cfluidic torque,xe2x80x9d provides power and communication necessary to operate downhole components. Excessive torque at high flow rates increases the wear on the rotatable components resulting in higher failure rates of the downhole tool.
What is needed is a technique for adapting components to the flow of fluid through the downhole tool. It is desirable that such techniques optimize the operation of the downhole components in response to the flow of fluid thereby providing control of the torque generated. It is further desirable that such techniques achieve one or more of the following, among others: provide adjustable torque rates responsive to increased flow rates, provide durability in even severe drilling environments, utilize passive and/or adjustable controls, provide adjustability to various flow ranges, prevent high speed and/or high torque failures, provide a wider range of flow rates, allow for the passage of large particles and/or larger volumes of fluid, resist erosion and prevent mechanical failures.
In order to reduce the torque at high flow rates, deformable components of a generator in a downhole tool, such as a rotor, stator and/or a turbine blade, are provided. The components adapt to the flow of fluid by deforming in response to the flow of fluid as it passes. The physical parameters of the components, such as dimension, camber angle and/or shape, and/or the materials of the component may be adjusted to allow the component to deform as desired. By controlling the deformation of the component, the desired torque of the generator may also be controlled. The rotatable elements of other components may also incorporate rotatable blades to control torque therein.
In at least one aspect the invention relates to a pressure pulse generator for a downhole drilling tool. The drilling tool has a channel therein adapted to pass drilling mud therethrough. The tool includes a rotor rotationally mounted to a drive shaft in the generator, and a stator positioned in the pulse generator such that rotation of the rotor relative to the stator creates pressure pulses in the drilling mud. At least one of the rotor, the stator and combinations thereof is selectively deformable in response to the flow of drilling mud through the generator whereby the torque is controlled.
In another aspect, the invention relates to a method of controlling fluidic torque in response to the flow of fluid through a downhole drilling tool. The method includes providing the downhole drilling tool with a generator having a rotor and a stator, positioning the downhole drilling tool into a wellbore, passing fluid through the generator at an initial flow rate, increasing the flow rate of the fluid passing through the generator, and deforming one of the rotor, the stator and combinations thereof from an original position to a deformed position in response to the increased flow rate.
In yet another aspect, the invention relates to a downhole drilling tool having a channel therein adapted to pass drilling mud therethrough. The tool includes a modulator positioned in the downhole tool, and at least one blade operatively connected to the modulator. At least one blade is rotatable in response to the flow of fluid through the drilling tool. At least one blade is adapted to selectively deform in response to the flow of drilling mud through the channel.
Empirical and/or numerical analysis techniques may be used to optimize the blade configuration and to develop a computational model to determine the material constants for given torque specifications. A fluid-structure interaction model may be used for computational analysis of an MWD axial turbine and its deformable blades. This model, typically a three-dimensional model, may be used for design and optimization of such blades.
Other aspects of the invention will be appreciated from the following description.